Project Summary The linker of nucleoskeleton and cytoskeleton (LINC) complex has emerged as an important mechanical intermediary between the nucleus and cytoskeleton. As its name describes, the LINC complex integrates force between the cytoskeleton and nucleoskeleton, and plays key roles in diverse aspects of cell behavior from positioning the nucleus to orchestrating cytoskeletal dynamics to modulating cell-cell and cell- matrix adhesions. In breast cancer, which we propose to study, numerous studies have found that at least one of the LINC complex components (Nesprin 2G, SUN2, or lamin A/C) is consistently downregulated. Furthermore, breast cancer cell nuclei are highly dysmorphic, often exhibiting abnormal grooves, clefts and folds in the nuclear envelope. These abnormal nuclei aid in grading the cancer and correlates with poor clinical prognosis. Collectively, all of these pieces of evidence suggest that a disproportionate amount of force is transmitted to breast cancer nuclei, and that the LINC complex likely plays a fundamental role. However, the basic function of the LINC complex and the consequences of its downregulation in cancer have not been studied. This lack of understanding is a critical barrier in the field that needs to be overcome. We hypothesize that differential expression of LINC complex proteins in breast cancer modulates force transmission to the nucleus, thereby altering mechano-chemical signaling and promoting a pathological phenotype. We propose to investigate how the LINC complex transmits force to the nucleus, and how changes in the LINC complex regulate the transition of normal breast epithelial cells into invasive breast cancer cells. We will employ a combination of molecular and physical techniques to analyze differences in molecular composition and nuclear force transmission by LINC complexes in normal and cancerous breast cells. Furthermore, we will examine the functional role of LINC complexes in breast cancer cells during 3D migration and in vivo metastasis.